(Meth)acrylic acid which is a main raw material of a superabsorbent polymer (SAP) is generally obtained by gas-phase oxidation reaction of propylene, etc.
For example, a raw material compound, such as propane, propylene, (meth)acrolein, etc., is subjected to gas-phase oxidation reaction in the presence of a catalyst to obtain a (meth)acrylic acid-containing mixed gas, which is then condensed or absorbed into an absorption solvent and collected as a (meth)acrylic acid-containing solution. From this (meth)acrylic acid-containing solution, low-boiling-point components such as the absorption solvent, (meth)acrylic acid dimers, (meth)acrylic acid oligomers, and high-boiling-point by-products such as maleic acid are separated by a series of purification processes to obtain crude (meth)acrylic acid.
A waste liquid obtained as a waste material in the process of separating the high-boiling-point by-products includes part of unrecovered (meth)acrylic acid, (meth)acrylic acid dimers, and high-boiling-point by-products such as maleic acid which are generated during the purification process.
In particular, it is known that a large amount of the (meth)acrylic acid dimers included in the waste liquid (hereinafter referred to as ‘(meth)acrylic acid waste liquid’) may be recovered as (meth)acrylic acid through a high-temperature or catalytic reaction.
Therefore, disposal of the (meth)acrylic acid waste liquid leads to a loss of (meth) acrylic acid, which is economically disadvantageous. For this reason, a variety of methods of stably recovering (meth)acrylic acid from the (meth)acrylic acid waste liquid have been suggested.
However, there are limitations in that most of the methods require complicated equipment and high energy consumption, and stability of the process operation is still low.